1. Field of the Invention
The field of the present invention is devices and methods relating to the collection of alveolar breath.
2. Background
Most human adults have a lung capacity of approximately 5-6 liters. Of this capacity, approximately only 0.3 liters is involved with the exchange of gases between blood and breath which takes place in the alveoli. Within this 0.3 liters, called the alveolar breath, oxygen and carbon dioxide rapidly diffuse across the epithelial membrane separating blood from breath due to concentration gradients existing between the blood and breath. As a result, the concentration of many gaseous constituents in the alveolar breath closely reflect the partial pressure of the same constituents in blood or reflect the presence of surrogates in blood from which the gas is derived.
Also present in alveolar breath are trace concentrations of molecules which are small enough to diffuse through the epithelial membrane. Some of these molecules have been shown to be indicative of disorders such as diabetes, lung cancer, renal failure, and asthma. Furthermore, depending on the severity of the disorder, such molecules may be present in alveolar breath in the parts per billion range (ppb) or in the parts per trillion range (ppt). Measurement of these trace components is therefore desirable for the early diagnosis of these disorders.
However, consistently collecting undiluted alveolar breath samples has proven to be a difficult task. During respiration, of the six liter total lung capacity, only 0.5 liters (called the tidal volume) is exchanged with the ambient atmosphere. However, this 0.5 liters is not the only constituent of a normally expired breath. The first part of expired breath consists essentially of air disposed in the mouth, nose, and upper respiratory tract. The next part of expired breath consists essentially of air from the bronchi and lower respiratory tract. Neither of these first two parts of expired breath exchange gases with blood. Therefore, the concentration of a particular gas in either of these two parts does not necessarily reflect blood content of that gas. The third and last part of expired breath consists essentially of alveolar breath.
Many devices exist in the prior art to collect alveolar breath samples. However, such devices tend to rely upon various different assumptions about breathing patterns to collect the alveolar breath sample. Unfortunately, these assumptions may lead to the collection alveolar breath samples which are diluted or the collection of breath samples which do not contain any alveolar breath.
For example, the device disclosed in U.S. Pat. No. 3,858,573 relies on the volume of a gas trap reservoir and the air pressure of an expired breath to capture an alveolar breath sample. The ""573 device consists of a gas trap reservoir having pressure sensitive valves enclosing each end, one acting as an inlet and the other acting as an outlet. Breath is expired through the inlet valve, with the pressure of the expired breath displacing any gas or breath inside the gas trap reservoir and forcing it through the outlet valve. This gas displacement continues until the breath is completely expired. Alveolar breath, being the last part of the expired breath, is trapped in the reservoir. The ""573 device and others like it rely on the assumption that alveolar breath is always expired. However, if the full tidal volume of breath is not expired, then alveolar breath either is never expired or is only partially expired. Thus, at times a partial alveolar breath sample is collected, such a partial sample being diluted with non-alveolar breath, or no alveolar breath is collected because none was actually expired. U.S. Pat. No. 5,211,181 discloses a device which is different from the ""573 device, but relies on the same assumptions about expired breath to collect an alveolar breath sample.
Another device for collecting an alveolar breath sample is disclosed in U.S. Pat. No. 5,361,772. This device consists of a small collection chamber with caps on each open end that are manually actuated to close the openings and trap an alveolar breath sample. The ""772 device relies on the small size of the chamber and the displacement of breath as it is expired through the chamber to trap alveolar breath. However, in many instances the ""772 device may be undesirable because it requires manual actuation to trap the alveolar breath sample. Therefore, the individual actuating the device, who may be different from the individual exhaling into the device, must necessarily guess as to when the expired breath consists of alveolar breath. The result of such a required method of operation is that an undiluted alveolar breath sample may not always be trapped in the collection chamber.
Yet another device used to collect an alveolar breath sample is disclosed in U.S. Pat. No. 4,297,871. This device monitors the flow rate of expired breath as it passes through part of the device. When the flow rate drops below specified threshold, the alveolar breath sample is drawn into a reservoir for analysis. The ""871 device operates on the assumption that when the flow rate of an expired breath drops below a predefined value, alveolar breath is present to be collected. Such an assumption, however, does not take into account normal variations in breathing patterns. For example, if breathing is stopped midway through an exhale, the device will sense a decrease in air flow and collect a breath sample. Under these circumstances, the breath sample collected will likely consist of either diluted alveolar breath or non-alveolar breath.
Thus, because of shortcomings in the prior art devices, an improved alveolar breath collection device is needed which can repeatedly and reliably collect an undiluted alveolar breath sample every time alveolar breath is expired. Such a device should be capable of adapting to the breathing patterns among different individuals and the breathing patterns of a single individual over the period of several breaths.
The present invention is directed to a device and method for collecting alveolar breath. The alveolar collection device comprises a hollow body having an inlet and two outlets. A first valve is disposed in the first outlet and a second valve is disposed in the second outlet. A collection reservoir is affixed to the hollow at the second outlet. A gas concentration monitor is operatively affixed to the hollow body to monitor the concentration of a specific gaseous component in expired breath passing through the hollow body. When the concentration of the specific gaseous component indicates that alveolar breath is present in the hollow body, the monitor actuates the second valve to an open position.
In practicing the method of this invention, expired breath is passed into the hollow body through the inlet and out of the hollow body through the first valve disposed in the first outlet. The concentration level of a specific gaseous component is monitored as the expired breath passes through the hollow body to determine when alveolar breath is present in the hollow body. When alveolar breath is present in the hollow body, the second valve, which is disposed in the second outlet, is actuated to divert the alveolar breath out of the hollow body and into a collection reservoir.
Thus, in a first separate aspect of the present invention, the alveolar collection device comprises a hollow body having an inlet, a first outlet with a first valve disposed therein, and a second outlet with a second valve disposed therein. A collection reservoir is affixed to the hollow body at the second outlet. A gas concentration monitor is operatively affixed to the hollow body to monitor the concentration of a specific gaseous component of expired breath. When the concentration of the specific gaseous component indicates that alveolar breath is present in the hollow body, the monitor actuates the third valve to an open position, thus collecting the alveolar breath in the collection reservoir.
In a second separate aspect of the present invention, the monitor compares the concentration of the specific gaseous component to a predetermined threshold concentration to determine when alveolar breath is present in the hollow body
In a third separate aspect of the present invention, the first valve comprises a one-way pressure sensitive valve.
In a fourth separate aspect of the present invention, the second valve is biased in the closed position.
In a fifth separate aspect of the present invention, heating elements are disposed on one or more surfaces of the hollow body to prevent the condensation of the expired breath passing through the hollow body.
In a sixth separate aspect of the present invention, a third valve is disposed in the inlet, the third valve being a one-way pressure sensitive valve.
In a seventh separate aspect of the present invention, the collection reservoir is detachably affixed to the hollow body.
In an eighth separate aspect of the present invention, any of the foregoing aspects may be employed in combination.
Accordingly, it is an object of the present invention to provide an improved apparatus and method for collecting an alveolar breath sample. Other objects and advantages will appear hereinafter.